Targeting Tumour Vasculature with Oncolytic Viruses

Abstract

Oncolytic viruses (OVs) have been engineered or selected for cancer cell-specific infection; however, we have found that following intravenous administration of vesicular stomatitis virus (VSV), tumour cell killing rapidly extends far beyond the initial sites of infection. This Bystander Effect is due to the virus’ ability to specifically target tumour vasculature through tumour-specific infection of tumour endothelium and the induction of an inflammatory response resulting in tumour-restricted coagulation, acute vascular disruption, apoptosis and necrosis of the tumour core. VSV-infected tumours, reconstructed in three-dimensions from serial histological sections, revealed that the majority of the tumour mass lacks significant blood flow in contrast to uninfected tumours, which exhibit relatively uniform perfusion. VSV infection rapidly induced intravascular coagulation within 6 hours of intravenous administration. The induction of coagulation was dependent on neutrophils and could be prevented with inhibitors of the coagulation pathway. Normal vasculature was not infected by VSV and no increase in coagulation was observed. Vascular collapse was also observed with the oncolytic poxvirus, JX-594, in patients and preclinical models. Biopsies from patients enrolled in a dose escalation trial for JX-594 were immunoreactive for vaccinia antigens and transgene products in high dose cohorts. Tumour-associated vessels from patients treated with JX-594 were infected with JX-594 and expressed virally encoded transgenes. A decrease in blood flow was also observed 5 days post infection. Several viruses, VSV, JX-594, vvDD, Maraba, and Sindbis, were able to rapidly induce widespread bystander cell death in a subset of mouse models. Tumours responded to OV therapy in three ways, and the type of response was determined by two factors - susceptibility to infection and the heterogeneity of the tumour microenvironment. Heterogeneity correlated with E-cadherin expression. Among tumours that supported viral replication, cancers with low E-cadherin expression were susceptible to vascular collapse. E-cadherin positive tumours were susceptible to infection and direct cell killing but resistant to vascular disruption or bystander cell death. If poorly-differentiated tumours were resistant to infection, no acute cell killing was observed. These histological subtypes provide a potential framework for the rational selection of patients, the integration of combination therapies and the creation of designer viruses to improve the success of OV therapy.